The invention concerns a tracking circuit for guiding a beam of light along the data tracks of a recorded medium that reflects the beam to a photodetector, the output voltage of which is supplied to a servo component through a variable-gain amplifier.
Tracking circuits of this type are employed for example in the optical scanning systems of compact-disk players for guiding beam of light that reads the information along the spiral data tracks of the compact disk.
Optical scanning systems for compact-disk players, which are frequently called optical pick-ups, are described and illustrated on pages 209 to 215 of Electronic Components and Applications, Vol. 6, No. 4, 1984.
The beam of light, which is emitted by a laser diode, is focused on the compact disk by lenses and reflected thence onto a photodetector, from the output signals of which not only the data stored on the disk but also the actual values for the tracking and focusing circuits are obtained. The focusing circuit focuses the beam of light emitted by the laser diode on the disk, and the tracking circuit guides it along the tracks on the disk. The actual value of the tracking circuit, which is called the radial-tracking error in the aforesaid reference, is supplied to the input terminal of a variable-gain amplifier, the output terminal of which is connected to a servo component. The servo component, which is usually called a radial drive, moves the optical scanning system radially over the disk, so that the beam of light emitted by the laser diode can be precisely guided along the data tracks and information stored on the disk can be read out.